Fuel-air ratio control for supercharged engines

ABSTRACT

A fuel-air ratio control device for a super-charged engine having a governor means connected to a fuel-adjusting member and a supercharger for supplying air through an intake manifold. The control device is directly engageable with the fuel-adjusting member and is responsive to intake manifold air pressure and to engine oil pressure. The device is inoperative to restrain the adjusting member during start-up of the engine and remains so until such time as a predetermined intake manifold pressure is attained at which time the control device moves to a position which permits the metering of engine oil therethrough to permit normal governor operation and proportional increases of fuel with air pressure increases. The control device is automatically shiftable to a position which blocks the metering of engine oil therethrough and which provides a hydraulic lock and positive connection between the control device and the fuel adjusting member to preclude any undesired increase of fuel supply.

Crews et a1;

1 1 Mar. 5, 1974 1 FUEL-AIR RATIO CONTROL FOR SUPERC HARG ED ENGINES[75] Inventors: Donald R. Crews, Peoria; Larry A.

Larson, East Peoria, both of 111.

[73] Assignee: Caterpillar Tractor Co., Peoria, 111.

[22] Filed: May l9, I972 [2]} Appl. No.: 254,852

Primary Examiner-Laurence M. Goodridge Attorney, Agent, or Firrri'Fryer,Tjensvold, Feix, Phillips & Lempio 57 ABSTRACT A fuel-air ratio controldevice for a super-charged engine having a governor means connected to afueladjusting member and a supercharger for supplying air through anintake manifold. The control device is directly engageable with thefuel-adjusting member and is responsive to intake manifold air pressureand to engine oil pressure. The device is inoperative to restrain theadjusting member during start-up of the engine and remains so until suchtime as a predetermined intake manifold pressure is attained at whichtime the control device moves to a position which permits the meteringof engine oil therethrough to permit normal governor operation andproportional increases of fuel with air pressure increases. The controldevice is automatically ,shiftable; to a position which blocks themetering of engine oil therethrough and which provides a hydraulic lockand positive connection between the control device and the fueladjusting member to preclude any undesired increase of fuel supply.

13 Claims, 3 Drawing Figures PATENTED 5197.4

SHEEI 1 BF 2 PATENTED 3.795.233

sum 2 or z FUEL-AIR RATIO CONTROL FOR SUPERCHARGED ENGINES BACKGROUND OFTHE INVENTION This invention relates to a fuel-air ratio control devicefor overriding an engine governor means to preclude an increase of fuelto the engine during a reduction of air pressure in the engine intakemanifold. Supercharged engines, and, in particular, engines withexhaust-driven supercharges will produce heavy and objectionable exhaustsmoke emissions when rapidly accelerated. This is because the enginesfuel-adjusting member can be advanced faster than the speed of theengine, and the supercharger can build up to provide sufficient air forthe combustion of all the fuel being injected. This results in theexpulsion of large quantities of unburned fuel as exhaust smoke.

Additionally, engines equipped with superchargers of the above typesmoke badly under lug. Lug is encountered when resistance or load on theengine is increased to the extent that engine speed is reduced belowthat which is indicated by the governor setting. Under these conditions,the engine governorattempts to regain the engine speed indicated by thegovernor setting by automatically advancing the engine fuel rack tosupply more fuel, but, due to the reduction in supercharger speed causedby the reduced engine speed, insufficient air is supplied to the engineto support complete combustion of the additional fuel 'being injected.

The patent to Parks, US. Pat. No. 2,767,700,0f common assignmentherewith, teaches a system intended to overcome the above problems byutilizing a pressure-responsive mechanism which is opposed by a springmember and which interacts with and restrains a fuel-adjusting memberthrough a movable stop. As disclosed in the Parks patent, a lack ofinlet manifold pressure allows the spring member to move the movablestop and, therefore, the .fuelcontrol member toward a decreased-fuelposition. Asinlet manifold air pressure increases, thepressure-responsive mechanism compresses the spring member and the maingovernor spring is permitted to move the movable stop and fuel adjustingmember toward an increased fuel position.

While theoretically operable, it has'been found that this type offuel-air ratio control imposes certain restrictions on overall engineperformance. First, it is difthan that of the governor spring and a stopmeans must be utilized to establish the predetemiined preload. Thefuel-adjusting member is permitted to move toward an increased fuelposition prior to engaging the movable stop. While allowing the governorspring to move the fuel control member to an increased fuel position,the spring member provides sufficient restraint until its force againstthe fuel control member is counteracted by increasing inlet manifold airpressure. Thus, a compromise between engine acceleration and enginesmoke is produced.

Also, in certain conditions such as when accelerating from a low speed,light load, it is characteristic for the supercharger to lag insupplying air to the intake manifold. This results in the production ofa negative pressure in the intake manifold. The fuel-air ratio controldevice of the above-designated patent could not respond to such negativemanifold pressure because the pressure-responsive mechanism therein isnormally disposed against an adjustable stop which is initially used toestablish the preload force of the spring member.

US. Pat. No. 3,077,873 to Parks et al., of common assignment herewith,overcomes some of the abovenoted disadvantages by providing a servomechanism ficult to provide sufficient fuel for starting bec'ausethespring member holds the movable stop and fueladjusting member toward thedecreased fuel position. Second, the governor spring must be allowed toperform its primary purpose of moving the fuel-adjusting member towardthe increased fuel position to maintain engine speed with an increasingload or to increase engine speed. At the same time, the spring memberwhich interacts with the pressure-responsive mechanism must providesufficient force to restrain' the governor spring until thepressure-responsive mechanism is actuated by inlet manifold airpressure. lf the preload force on the spring member is greater than thaton the governor spring, acceleration of the engine will be impeded to anextent which is detrimental to engine performance. If the spring memberpreload force is less than that on the governor spring, the fuel controlmember will not be positively restrained by the movable stop andacceleration will be increased, but overfueling and, therefore,objectionable smoke will occur. Thus, the initial preload force on thespring member must be made greater which has a movable member actingupon a valve member while a pressure-responsive mechanism acts upon avalve spool. Hydraulic fluid pressure is utilized to provide a balanceof forces between the governor spring, spring member and the intake airpressure responsive mechanism. The use of the servo unit permits thespring member to be balanced for improved response when interacting withthe pressure-responsive mechanism. However, the main disadvantage ofthis device lies in the necessary maintenance of a servo piston as aseparate unit and in the use of an intermediate movable member toprovide control of the valve. The resultant configuration is complex andrelatively costly.

SUMMARY AND OBJECTS OF THE INVENTION A fuel-air ratio control device forsupercharged engines having a governor connected to a fuel controlmember and a supercharger supplyingair through an intake manifold to theengine having'an integral servo piston and valve unit placed inarestraining relationship with respect to the fuel control member. Theservo pistonis activated by a fluid force controlled by movement of avalve spool which slides in an opening and closing manner relative toports in a portion of the servo piston. The valve spool is secured to apressureresponsive mechanism which communicates with the engine intakemanifold. Resilient means oppose the reaction of the pressure-responsivemechanism to intake manifold pressure. During engine start-up, the valvespool and ports of the servo piston are in an open condition to renderthe servo unit inoperative and to permit unrestricted operation of thefuel control member. The servo unit is subsequently activated when apredetermined increase in manifold air pressure shifts the valve spoolrelative to the servo piston ports and blocks and meters the flow ofhydraulic fluid to the servo piston. During subsequent reductions inmanifold air pressure, the servo unit is effective-to restrain the fuelcon-- trol member against movement toward an increased fuel position.The servo units restraint of the fuel control member precludes anydisproportionate increases in fuel to the engine when the air availablein the intake manifold is insufficient to support proper fuelcombustion.

It is an object of this invention to provide an improved fuel-air ratiocontrol device for overriding the governor and controlling the injectionof fuel to a supercharged engine in strict proportion to the airpressure available in the engines intake manifold to insure completecombustion of fuel by the engine.

Another object of this invention is to provide an improved governoroverriding fuel-air ratio control device which is responsive to bothintake manifold air pressure and to engine oil pressure with the controldevice automatically permitting unrestricted movement of the fueladjusting member on the engine during cranking to insure sufficient fuelfor dependable starting, but thereafter automatically restricting theinjection of fuel into the engine to precisely that amount required foroperating the engine at maximum efficiency.

Other objects and advantages of the present inven-- tion will becomemore readily apparent upon reference to the accompanying drawings andfollowing description.

BRIEF DESCRIPTION OF THE DRAWINGS through a modified embodimentof thefuel-air ratio control device of the instant invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring particularlyto FIGS. .'1 and 2 in the drawings, a fuel pump has a plunger 12vertically reciprocal during engine operation to supply fuel through afuel injection line 11 to one of the cylinders of the engine, therebeing one pump for'each engine cylinder. Longitudinal movement of a fueladjusting member 17 having rack teeth 15 moves a gear 14 secured toplunger 12. The pump is of the metering type in which angular adjustmentof the plunger l2 results in a variation of the quantity of fuelinjected upon each stroke.

The fuel adjusting member 17 is secured to a riser 18 having anextending link 19 with a stop member 20 attached to its distal end. Apair of flyweights 22 carried upon a yoke 23 are driven by a gear 24which is rotated by the engines timing gear (not shown) at a speed pro.-portional to engine speed. Radially, outward movement of the flyweightsdue to centifugal force causes portions of the flyweights to actleftwardly upon the riser 18. A

spring 26, disposed between the riser and a collar 27,

opposes the biasing action of the flyweights. A movable lever 28 ispositioned to provide a predetermined selectable preload force for thespring 26 to act against the force of the flyweights 22.

An engine air intake manifold 30 is supplied with air under pressure byan engine-driven supercharger 31. A conduit 32 communicates between theintake manifold and a chamber 35 formed by an adapter 33 having a cover36 secured by bolts 37.

A control housing 39 has an inlet 40 connected to a fluid pressuresource such as enginelubrication oil. An orifice 43 communicates inlet40 with a bore 44 formed in the housing 39. A servo unit 46 has a pistonportion 47 slidable within bore 44 and a valve means 48 integral with apiston portion and slidable within a bore 50 formed in the housing. Thevalve means has an extending portion 49 with a shoulder 49a thereonwhich is positioned to engage the stop member 20 under conditions to beexplained hereinafter. An expansible chamber 53 is formed by a face 51of the piston 47, a surface 52 of housing 39, and bore 44. Fluid frominlet 40 is permitted to enter chamber 53 by way of a groove 54 in thesurface 52 which is intersected by the orifice 43.

A first set of passages 56 in valve means 48 communicate the chamber 53with a bore 62 in the servo unit. A second set of passages 57 of valvemeans 48 comm unicate the bore 62 with an annular groove 58 formed inthe bore50. The annular groove, in turn, is inter-' sected by a drainpassage 60 inhousing 39. Another passage 91 is provided to communicateany fluid which might leak through the servo unit to the drain.

A valvevspool 63, slidable in the bore 62, has an annulus 66 formedbetween a pair of lands 64 and 65. When the land 64 is disposed as shownin FIG. 1, the passage 56 is open and land 65'is disposed so thatpassage 57 is open and chamber 53 is in communication with the drainpassage 60. l

A threaded portion 67 of valve spool 63 is secured to a cup member 68.An end 69 extends from the threaded portion 67 and has a pin 70 whichengages a slot 36a in the cover 36.

A first spring member 72, having a first spring rate, is disposedbetween the piston 47 and cup member 68. A second spring member 73,having a second spring rate, is disposed between the cup member and aseat member 74. A diaphragm 76 is secured between the adapter 33 and thehousing 39 and is supported by the cup member 68. A washer 77 disposedadjacent to and rearwardly of the diaphragm 76 acts as a seat for athird spring member 78 which resides between the cover 36 and thewasher. The rates of the three spring members are such that forces onthe diaphragm are balanced -when no pressure is extant in the chamber 35to pro vide sensitivity in the servo unit.

OPERATION Prior to engine start-up, the fuel-air ratio control of thepresent invention assumes an inoperative position in the followingmanner. Spring member 72 urges the servo unit 46 toward the right, asshown in FIG. 1, and removes the shoulder 49a from engagement with stop20. Any movement of the lever 28 in a counterclockwise directioncompresses spring 26 and moves the fuel adjusting member 17 rightwardlytoward an overfueling position. During engine cranking or upon initialstart-up of the engine, the valve spool 63 is maintained in thisposition which provides communication be tween passages 56 and 57through annulus 66 by means of the balanced condition of the springmembers 73 and 78 which act upon the diaphragm 76. Fluid under pressurewhich enters the chamber 53 from the inlet 40 is drained off throughpassages 56, 57, and 60 thus preventing the exertion of a fluid forceupon the piston 47 and consequent leftward movement.

At such time, diaphragm 76 is acted upon by the inv creasing airpressure in chamber 35. This tends to compress the spring members 72 and73 and to move valve spool 63 toward the right. Such movement eventuallycauses the land 64 to cover passages 56. Fluid is thus prevented fromdraining from the chamber 53 and fluid pressure begins to build thereinto force the piston 47 toward the left into a control operativeposition. During this leftward movement, the shoulder 49a engages stopmember and moves the fuel-adjusting member 17 to a decreased fuelposition suchas is shown in FIG. 2. The mechanism is cocked andoperative when it is disposed as shown in FIG. 2. 7

When the engine is operating at idle, air pressure in the intakemanifold and in chamber 35 together with the bias of spring member 78would not be sufficient to overcome the bias of the spring members 72and 73 acting upon the diaphragm 76. The valve spool 63 would'berestrained in a leftward position bythe diaphragm member 76 and thepiston 47 would be in the operative position wherein land- 64 wouldeffectively restrict the passages 56 to permit only a predeterminedamount of fluid to be metered from chamber 53 to maintain the piston 47in the position shown in FIG. 2. The passages 57 would be out ofalignment with the annular groove 58 and the drain passage 60 to preventfluid drainage.

As previously described, when the lever 28 is moved counterclockwise,the spring 26 is compressed to cause loading and movement of thefuel-adjusting member 17 rightwardly toward an increased fuel position.However, with the fuel-air ratio control device operative,

the spring members 73 and 78 would tend to position the valve spool 63toward the left. Therefore, the servo unit 46 and the shoulder 49a wouldpermit only a slight movement of the fuel control member toward theincreased fuel position. e

If a negative pressure occurred momentarily in the manifold and chamber35, such as when the engine was. acceleratingfrom a low speed atflightload, the diaphragm 76 would be drawn to the left causing the servo unit46 to be moved slightly in the same direction. The shoulder 49a wouldengage the stop 20 as the stop tended to move rightwardly to increase,the fuel supply to meet the demands. -As engine speed increased,however, air pressure in chamber would increase slightly and would movethe diaphragm 76 and valve spool 63 to the right. The land 64 would moveand slightly uncover the passages 56 to permit fluid to be metered outthe opening and drain to the outlet 75through a passage 74a. Fueladjusting member 17 would then be permitted to pull the servo unit tothe right as long as the air pressure in chamber 35 was increasing andthe valve spool 63 was moved rightwardly to allow fluid to drain.

amount so as to cause land 64 to restrict the passages 56 and allowfluid forces in chamber 53 to move the piston 47 slightly leftwardly tocause shoulder 49a to restrain the stop 20 and prevent adisproportionatelylarger amount of fuel to be injected relative to theavailable air. If the operator moves the lever 28 to accelerate theengine, the stop 20 will be restrained by shoulder 4% until such time assufficient air becomes available in chamber 35 to permit the servo unit46 to be moved to the right by the fuel-adjusting member 17.

DESCRIPTION OF MODIFIED EMBODIMENT A modification of the instantinvention is shown in FIG. 3. A different plurality of spring membersare provided to oppose the air-pressure-responsive diaphragm 76 in amanner somewhat similar to the first form of the invention. Elementscommon to both forms haveidentical reference numerals. The modificationpermits a variable biasing force to act upon the diaphragm for' moreprecise tailoring of the fuel-air ratio control device to the needs of aparticular engine, as will be described.

The spring rateof a single spring opposing the pressure-responsivediaphragm is linear. However, the intake manifold pressure of asupercharged engine does not always increase at a linear rate. Such arate disparity could lead to short periods when the increasing airpressure is temporarily reduced while the fuel-adjusting member ismoving toward an increased fuel position. This could lead to aphenomenonreferred to as secondary exhaust smoke plumes. The fuel-airratio control device, shown in the version of FIGS. 1 and 2, eliminatesor limits these secondary plumes to acceptable limits in most engines.It has been found, however, that in certain engines the exhaust plumesare slightly above an acceptable limit. For these engines, it becomesnecessary to provide a plurality of springs in series or a variable-ratespring to oppose'the pressure-responsive diaphragm. With this provision,it is possible to tailor the fuel-air ratio control device functions toparticular engine characteristics.

As "shown in FIG. 3, a first spring member 80 is disposed between a seatmember 81 and the piston 47. Seat member 81 is slidable within a bore 82in the housing 39. A second spring member 84 is disposed between theseatmember 81 and an intermediate cupshaped'member 85. Av third springmember 86 is disposed between a flange 88 of the cup-shapedmember and acup member 68. A fourth spring member 78 is disposed between the cover36 and the washer 77, as

' in the primary embodiment. Each spring member has a particularpredetermined spring rate. I

For instance, the rate required of the third spring member 86 iscalculated by determining the amount of rack movement (deflection)relative to the force (load) acting on the diaphragm 76 during a givenperiod of engine operation. A spring equation, Deflection (third .springmember) (Load/K4 K3) is used where K4 (of second spring member)=[Load/K4(l/ 1/K2 l/K )l where K4, deflection, load and K3 (third spring member)are know establishes the rate of the second spring member K2. The raterequired of the first spring member is calculated by the amount ofdeflection relative to the load acting on diaphragm 76 just prior tothat period controlled by the second spring member. Spring equation,Deflection (of first spring member)= [load/K4 (l/l/Kl l/K2 l/K3)] whereK4, deflection, and load are known, and K3 and- K2 have previously beendetermined establishes the rate of the first spring member K1.

OPERATION OF MODIFIE D EMBODIMENT In operation, the first spring member80, with a relatively low rate, is utilized initially to move the seat81 slidably toward the left within the bore 82. Thus, initial airpressure in the chamber 35, which would be slight, would be workingagainst a relatively weak spring. As air pressure increased further, thespring members 85 and 86, having relatively higher forces than springmember 80, would act against thespring 80 through the seat member 81until the seat member would move against a stop 83, at which time thesecond spring member 84, having a slightly greater spring rate than thespring member 80, would oppose the air pressure in chamber 35. A stillfurther increase in air pressure in the chamber 35 would compressthespring member 84 through the spring member 86, which member has a stillhigher spring rate than spring member-84. At a predetermined airpressure in chamber 35, cup-shaped member 85 will bottom against seatmember 81 and air pressure in chamber 35 will'begin to act upon thespring member 86. Thus, a selectively, progressivelyincreasing springrate will be available to oppose the variably-increasing air pressure inchamber 35.

In the primary embodiment the use of a single spring produces a linearforce to oppose the variablyincreasing air pressure force. In themodified embodiment the use of different rate springs providesra linearforcein combination with a geometric change of force to more evenlymatch the change of force of the air pressure. I I

Valve spool 63 will act in the manner previously described in theprimary embodiment. Compression of the springs by thepressure-responsive diaphragm will act to permit fluid to be metered outof chamber 53 This will permit the fuel-adjusting member 17 to moverightwardly toward an increased fuel position. The plurality of springspermits the pressure-responsive diaphragm to be more responsive to theair pressure characteristics of the supercharger.

While the invention has been described and shown with particularreference to the preferred embodiment, it will be apparent thatvariations and modifications would fall within the spirit of the presentinvention and the scope of the appended claims.

What is claimed is:

1. In an engine having an intake manifold, a governor-controlled fuelsupply means, said fuel supply means having a control member'meansadapted to move in a first direction to increase the supply of fuel tothe engine and in a second direction to decrease the supply of fuel tothe engine, and override means for selectively overriding said governorto prevent movement of said control member means in said firstdirection,

8v said override means comprising; a piston means slidable within afirst chamber means, a portion of said piston means being capable ofdirectly contacting a portion of said control member means to preventmovement of said control member means, diaphragm means movable within asecond chamber means within said override means, first resilient biasingmeans physically disposed between said piston means and said diaphragmmeans for acting upon and biasing said piston means toward said firstdirection and for acting upon and biasing said diaphragm means towardsaid second direction, means for supplying fluid pressure to said firstchamber means to move said piston means toward said second directionagainst the bias of said first resilient means, valve passage means insaid piston means for selectively draining off said fluid pressure fromsaid first chamber to allow said piston means to move in said firstdirection, valve spool means connected to said diaphragm means forselectively opening and closing said valve passage means, means forcommunicating said intake manifold to said second, chamber means tosupply intake manifold pressure thereto to move said diaphragm means andsaid valve spool means toward said first direction in opposition to saidfirst resilient biasing means, second resilient means separate from saidfirst resilient means for acting upon said diaphragm means and biasingsaid diaphragm means and said valve spool means toward said firstdirection, and third resilient means separate from said first and secondresilient means for biasing said diaphragm means and said valve spoolmeans in said second direction.

2. The override means of claim I wherein the biasing force exerted uponsaid diaphragm means'by said second resilient means is substantiallybalanced by the opposing forces exerted upon said diaphragm means bysaid first and third resilient biasing means 3. The override means ofclaim I wherein fourth resilient biasing means are provided for biasingsaid diaphragm means toward said second direction.

4. The override means of claim 3 wherein said first, third and fourthresilient biasing means act in series upon said diaphragm means inopposition to the biasing forces exerted upon said diaphragm means bysaid sec ond resilient biasing means and said intake manifold pressureextant in said second chamber means.

5. A fuel-air ratio control device for an engine having agovernor-controlled, fuel-adjusting member means and a-supercharger tosupply air through an intake manifold to the engine comprising;resilient means responsive to intake manifold air pressure, valve meansfor interacting with said resilient means and for movement responsive toengine lubrication fluid pressure toward and away from said resilientmeans during normal governor-controlled engine operation, said valvemeans being selectively engageable in interfering relation with saidfuel-adjusting member means for constraining movement of saidfuel'adjusting member means upon a reduction in manifold air pressurebut for disposition in non-interfering relation with said fueladjustingmember means during cranking of the engine so that sufficient fuel issupplied to said engine upon starting in accordance with requirementsset by the governor, said valve means also being effective subsequent tostart-up for interfering with'said fuel-adjusting member means to assureoptimum fuel-air ratio for said engine and to prevent overfueling duringperiods of reduced pressure in said intake manifold, said resilientrelation with said fuel-adjusting member means untilsaid valve spoolmeans is moved in a first direction, chamber means'for receiving enginelubrication fluid under pressure to urge said piston in a seconddirection, means communicating between said chamber means and said valvespool means wherein initial movement of said valve spool means in thefirst direction permits said piston means to beurged in the seconddirection and movement of said valve spool means in the second directionprevents said piston means from moving in the first direction and causessaid piston means to engage said fuel-adjustingmemb er means ininterfering relation therewith.

7. A fuel-air ratio control device for an engine having agovernor-controlled, fuel-adjusting member means and a superchargerwhich supplies air-through an intake manifold to the engine, saidcontrol device comprising; pressure-responsive means in communicationwith said intake manifold, servo unit meansfor engagement'with saidfuel-adjusting member mea'n'sand for actuation by engine lubricantpressure and having an integral piston portion and valve portion, saidvalve portion of said servo unit means having a bore and port means, avalve spool means connected to saidpress ureresponsive. means andslidably disposed within said bore and having an annulus for cooperatingwith said port means in a sliding relation thereto for controlling theflow of engine lubricant to actuate said servo unit means, resilientmeans on one side of said pressureresponsive means for positioning saidannulus with reres pect to said spect to said port means to permitsubstantially unrestricted flow of lubricant through said servo unitmeans during engine start-up to render said servo unit means inoperativeand to permit unrestricted operation of said fuel-adjusting membermeans, said servo unit means being subsequently actuated upon apredetermined increase in manifold air pressure at which time saidpressure-responsive means and said valve spool means are shiftedrelative to said port means to restrict and meter the flow of lubricantthrough said servo unit means so that during any subsequent reduction inmanifold air pressure said servo unit means is effective to restrainsaid fuel-adjusting member means against movement to preclude anydisproportionate increase in fuel supply to the engine as determinedwith respect to the air available in the intake manifold.

8. The fuel-air ratio control device of claim 7 wherein the said servounit means has an extended member which has a stop means for selectivelyconstraining said fuel-adjusting member means.

9. The fuel-air ratio control device of claim 7 wherein said servo unitmeans is disposed in substantially axial alignment with saidfuel-adjusting member means.

10. The fuel-air ratio control device of claim 7 including resilientmeans acting in opposition upon oppo- I site sides of saidpressure-responsive means and holding said pressure-responsive means ina normallybalanced condition.

ll. The fuel-air: ratio control device of claim 10 wherein said opposingresilient means are positioned in substantially axial alignment withsaid servo unit means and fuel-adjusting member means. i

12. The combination of claim llv wherein said resilient means includespring means having a selectivelyvariable spring rate.

13. The combination of claim 12 including a plurality of spring means,said spring means being activated cumulatively and in a series by saidpressure-responsiv

1. In an engine having an intake manifold, a governor-controlled fuelsupply means, said fuel supply means having a control member meansadapted to move in a first direction to increase the supply of fuel tothe engine and in a second direction to decrease the supply of fuel tothe engine, and override means for selectively overriding said governorto prevent movement of said control member means in said firstdirection, said override means comprising; a piston means slidablewithin a first chamber means, a portion of said piston means beingcapable of directly contacting a portion of said control member means toprevent movement of said control member means, diaphragm means movablewithin a second chamber means within said override means, firstresilient biasing means physically disposed between said piston meansand said diaphragm means for acting upon and biasing said piston meanstoward said first direction and for acting upon and biasing saiddiaphragm means toward said second direction, means for supplying fluidpressure to said first chamber means to move said piston means towardsaid second direction against the bias of said first resilient means,valve passage means in said piston means for selectively draining offsaid fluid pressure from said first chamber to allow said piston meansto move in said first direction, valve spool means connected to saiddiaphragm means for selectively opening and closing said valve passagemeans, means for communicating said intake manifold to said secondchamber means to supply intake manifold pressure thereto to move saiddiaphragm means and said valve spool means toward said first directionin opposition to said first resilient biasing means, second resilientmeans separate from said first resilient means for acting upon saiddiaphragm means and biasing said diaphragm means and said valve spoolmeans toward said first direction, and third resilient means separatefrom said first and second resilient means for biasing said diaphragmmeans and said valve spool means in said second direction.
 2. Theoverride means of claim 1 wherein the biasing force exerted upon saiddiaphragm means by said second resilient means is substantially balancedby the opposing forces exerted upon said diaphragm means by said firstand third resilient biasing means.
 3. The override means of claim 1wherein fourth resilient biasing means are provided for biasing saiddiaphragm means toward said second direction.
 4. The override means ofclaim 3 wherein said first, third and fourth resilient biasing means actin series upon said diaphragm means in opposition to the biasing forcesexerted upon said diaphragm means by said second resilient biasing meansand said intake manifold pressure extant in said second chamber means.5. A fuel-air ratio control device for an engine having agovernor-controlled, fuel-adjusting member means and a supercharger tosupply air through an intake manifold to the engine comprising;resilient means responsive to intake manifold air pressure, valve meansfor interacting with said rEsilient means and for movement responsive toengine lubrication fluid pressure toward and away from said resilientmeans during normal governor-controlled engine operation, said valvemeans being selectively engageable in interfering relation with saidfuel-adjusting member means for constraining movement of saidfuel-adjusting member means upon a reduction in manifold air pressurebut for disposition in non-interfering relation with said fuel-adjustingmember means during cranking of the engine so that sufficient fuel issupplied to said engine upon starting in accordance with requirementsset by the governor, said valve means also being effective subsequent tostart-up for interfering with said fuel-adjusting member means to assureoptimum fuel-air ratio for said engine and to prevent overfueling duringperiods of reduced pressure in said intake manifold, said resilientmeans comprises a diaphragm means of resilient flexible material and aplurality of separate spring means arranged on opposite sides of saiddiaphragm means in normally-balanced relationship to said diaphragmmeans and selectively acting to hold said valve means in saidnon-interfering position with respect to said fuel-adjusting membermeans.
 6. The control device of claim 5 wherein said valve meansincludes a piston means, a valve spool means connected to said diaphragmmeans, said valve spool means and said piston means being in anon-interfering relation with said fuel-adjusting member means untilsaid valve spool means is moved in a first direction, chamber means forreceiving engine lubrication fluid under pressure to urge said piston ina second direction, means communicating between said chamber means andsaid valve spool means wherein initial movement of said valve spoolmeans in the first direction permits said piston means to be urged inthe second direction and movement of said valve spool means in thesecond direction prevents said piston means from moving in the firstdirection and causes said piston means to engage said fuel-adjustingmember means in interfering relation therewith.
 7. A fuel-air ratiocontrol device for an engine having a governor-controlled,fuel-adjusting member means and a supercharger which supplies airthrough an intake manifold to the engine, said control devicecomprising; pressure-responsive means in communication with said intakemanifold, servo unit means for engagement with said fuel-adjustingmember means and for actuation by engine lubricant pressure and havingan integral piston portion and valve portion, said valve portion of saidservo unit means having a bore and port means, a valve spool meansconnected to said pressure-responsive means and slidably disposed withinsaid bore and having an annulus for cooperating with said port means ina sliding relation thereto for controlling the flow of engine lubricantto actuate said servo unit means, resilient means on one side of saidpressure-responsive means for positioning said annulus with respect tosaid port means to permit substantially unrestricted flow of lubricantthrough said servo unit means during engine start-up to render saidservo unit means inoperative and to permit unrestricted operation ofsaid fuel-adjusting member means, said servo unit means beingsubsequently actuated upon a predetermined increase in manifold airpressure at which time said pressure-responsive means and said valvespool means are shifted relative to said port means to restrict andmeter the flow of lubricant through said servo unit means so that duringany subsequent reduction in manifold air pressure said servo unit meansis effective to restrain said fuel-adjusting member means againstmovement to preclude any disproportionate increase in fuel supply to theengine as determined with respect to the air available in the intakemanifold.
 8. The fuel-air ratio control device of claim 7 wherein thesaid servo unit means has an extended member which has a stop means forselectively constraining said fuel-adjusting member means. Pg,23
 9. Thefuel-air ratio control device of claim 7 wherein said servo unit meansis disposed in substantially axial alignment with said fuel-adjustingmember means.
 10. The fuel-air ratio control device of claim 7 includingresilient means acting in opposition upon opposite sides of saidpressure-responsive means and holding said pressure-responsive means ina normally-balanced condition.
 11. The fuel-air ratio control device ofclaim 10 wherein said opposing resilient means are positioned insubstantially axial alignment with said servo unit means andfuel-adjusting member means.
 12. The combination of claim 11 whereinsaid resilient means include spring means having a selectively-variablespring rate.
 13. The combination of claim 12 including a plurality ofspring means, said spring means being activated cumulatively and in aseries by said pressure-responsive means.